Combination desulfurization and catalytic reforming process



Aug. 28, 1956 D. D. MacLAREN COMBINATION DESULFURIZATION AND CATALYTIC REFORMING PROCESS Filed March .'51, 1955 @omai d E. mal-clara@ {bnverzor Cltdtcnrrzmq1 y troleum hydrocarbons.

COMBINATION DESULFURIZATION AND i CATALYTIC REF ORlVIING PROCESS Donald D. `MacLaren, 'Scotch Plains, N. J., assigner to Esso Research and Engineering Company, a corporation of Delaware Application March s1, 195s, Serin No. 345,922

6 claims. (c1. 19a- 28) The present invention relates to the rening of pe- It further relates to a combination of relining steps for preparing the feed stock tota catalytic reforming operation whereby the reforming opera-tion` is maintained at a high level of conversion and selectivity. The present invention particularly concerns hydrocarbon feedstocks that boil within the range of about 100 to 500 F. and especially about 200 to 400 F. These feedstocks include light naphtha, heavynaphtha, and kerosene; and they may be additionally characterized by possessing critical temperatures falling Within the range of about 400 to 700 F. and especially about 500 to 650 F. The present invention alsofrelates to an improved process for desulfurizing petroleum fractions `of the -types dened above.

Catalytic reforming processes are widely used in the petroleum industry for the upgrading of various pe.

troleum fractions. They find particular application in the case of light and heavy virgin and/ or catalytic naphthas where they are employed for the purpose of increasing the locta-ne ratings of these fractions. These processes are especially desirable for the treatment of heavy virgin naphtha fractions.

Catalytic reforming processes that are used at the present time include hydroforming, platforming, and the like. In platforming, a virgin and/ or cracked naphtha is contacted with a platinum type catalyst at elevated temperatures of about 800 .to 1000 F., pressures of about 400 to 1,000 p. s. i. g. with hydrogen recycle rates of labout 3,000 to 12,000 s. c. f./.bbl. of feed, maintained by recycling'hydrogen-containing gas produced yin the process. Processes of this type and suitable` catalysts therefor are known in the art (see, for example, U. S. Patents Nos. 2,478,916, 2,479,409, 2,479,1'10, and Petroleum Processing, vol. 5, No. 4, pages 35l1 to 360).

lIn hydroforming, a virgin and/ or cracked naphtha is contacted in the presence of hydrogen-rich gas with such well known catalysts as molybdena on alumina which may or may not be stabilized with silica. Suitable reaction conditions include temperatures of about 800 to 1100 F. and pressures from about 50 to 1,000 p. s. i. g. with continuous or intermittent regeneration of the catalyst, as necessary, to remove car-bonaceous deposits therefrom. The regeneration phase of this process is conventionally carried out by controlled burning with air or mixtures of air and recycled ilue gas from the regeneration process. Regeneration temperatures are usually limited to between l000 and 1200 F.

nitecl States Patent() Widely used is hydrolining.

It will be noted that the various catalytic reforming It has been generally recognized that the catalysts employed in catalytic reforming processes are generally very sensitive to sulfur. It has been found that sulfur, either in the hydrocarbon feedstock or in the gas that "Ice is recycled to the reactor and in amounts as small as 0.41% by weight of the feed, acts as a catalyst poison and greatly reduces activity and selectivity. Minimizing the amount otr sulfur-containing compounds in catalytic reforming processes is thus highly desirable.

Sulfur occurs in virtually `all petroleum crude oils. In addition, the sulfur compounds boil throughout the boiling range of the crude oils. In general, a petroleum crude oil maycontain up to as high as 2 to 4 wt. per cent of sulfur. A light virgin naphtha boiling in the range of about yto 200 F. may contain up to about 0.1 wt. per cent sulfur, while a heavy virgin naphtha boiling from about 200 to 400 F. may contain up to about 0.3 to .5 wt. per cent of sulfur. 'Iihe sulfur in these instances is generally considered to be present in the form of ('1) acidic compounds such as hydrogen sullide and mercaptans, and (2) neutral compounds such as thiophenes, disultides, alkyl and cyclic sullides.

In view of the adverse effects that sulfur compounds have in catalytic reforming operations as well as in petroleum products, a number of desulfurization processes have been developed. One of the most widely used is one in which a hydrocarbon fraction is contacted with concentrated sulfuric acid. This process unfortunately has the undesirable property of degrading a part of the feedstock byforming sulfonates, polymers and the like. In view of these degradation reactions, it has been necessary to rerun orl redistill the treated hydrocarbon fraction in order to free the desired product from the degradationproducts.

Another desulfurization process that is becoming more In this process, a sulfurcontaining petroleum fraction is contacted with a catalyst such as cobalt molybdate on a carrier such as alumina at temperatures of about 500 to 700 F. and pressures of about 50 to 500 p. s. i. g. Tungsten and nickel suldes may also be employed as catalysts. The petroleum fraction is fed to the hydr-ofiining zone at rates of about 0.1 to 20 volumes of feed per volume of catalyst `per hour. Hydrogen gas is also passed through the hydrolining zone at rates of about 50 to 5000 s. c. f./bbl. of feed. "Under these conditions, some hydrogen is consumed by the process. Hydrogen consumption rates are generally in the range of about 1 to 20 s. c. f./ibbl. of feed but may be as high as 1150 to 600 s. c. f./ibb1. While the hydrolining process may be employed on petroleum fractions that exist within a hydrofining zone in either the liquid or vapor phase, the present invention has primary application to the processing .of those fractions that are present therein in the vapor phase. Substantial amounts of hydrocarbons in the liquid phase may, of course, also be present.

LIn the hydrolining process the sulfur compounds are largely converted to hydrogen sulfide. This hydrogen sulfide is conventionally separated from the hydroned product lby (l) condensing the eflluent from the hydroining zone and treating the condensate with caustic solution; (2) by scrubbing the vapors with caustic solution; or (3) by fractionation of the effluent. In all of these methods a large heat transfer surface is required between the hydrotining zone and any subsequent catalytic reforming oper-ation. In addition, a loss in heat level occurs. This requires additional heat transfer surfaces thereby adding to the cost of removing sulfur.

Accordingly, it is an object of the present invention to better utilize the hydroning process to reduce the sulfur content of the hydrocarbon feed stock to a catalytic Areforming operation. It is an additional object to eliminate the use of caustic Washing and distillation steps in removing hydrogen sulfide from the product stream of a hydroning unit. It is a particular object of the present process to conserve the sensible heat existing in the product stream of a hydroiining unit while reducing the sulfur content of the stream to the desired level. In the latter connection, it is a particular object of the present invention to reduce the sulfur content of the hydrocarbon feed to a catalytic reforming unit to a value of about 0.02 Wt. percent and preferably 0.01 wt. percent or less. It is also an object of the present invention to provide a combination process that incorporates hydroning and catalytic reforming steps for improving the octane quality and for lowering the sulfur content of petroleum hydrocarbon fractions boiling in the motor fuel boiling range.

These objectives are achieved by a combination of processing steps involving hydroiining, vapor-liquid separations under controlled pressures and temperatures, and catalytic reforming. Briefly, a sulfur-containing hydrocarbon mixture i-s introduced to a hydroning zone operating at a high enough pressure to keep the feed as a eliquid at slightly below its critical temperature. The temperature need not be limited to the critical at this point. Here the undesirable sulfur compounds are converted to hydrogen suliide which passes from the hydroflning zone in admixture with the hydrocarbons. The temperature of this mixture is `adjusted at substantially constant pressure to a value slightly below the critical temperature of the hydrocarbon mixture. It is preferred that the mixture be cooled not greater than about 50 F. below its critical temperature and preferably less than 25 F. below the critical. By employing these temperature differentials, it is considered that a major portion of the hydrocarbon constitutents will be liquefied and separated from the hydrogen sulfide. The resulting mixture of liquid hydrocarbons and hydrogen sulfide are then introduced within a high pressure separation zone where the vaporize materials are disengaged. The vaporized and liquid products are then removed las separate streams from the separation zone.

The temperature within the high pressure separation zone is preferably maintained as close to the critical as possible while still condensing a major portion of the desulfurized feed in order to retain as much of the sensible heat in the feed as possible.

The vapors leaving the high pressure separation zone are further cooled in one or more additional cooling zones to essentially atmospheric temperature. lThe condensed vapors are then flashed to atmospheric pressure, and essentially all of the hydrogen sulde is thereby separated from the liquid. The desulfurized liquid, repressured to the level of the reforming zone, is reheated by indirect heat exchange with the condensing vapors from the high pressure separator. This step is valuable in conserving the sensible heat content of the vapor stream.

The pressure of the liquefied hydrocarbons withdrawn from the high pressure separation zone is adjusted to the level entering the catalytic reforming zone. The liquid streams from the high and low pressure separators are combined, preheated, and then introduced within the catalytic reforming zone.

As mentioned earlier, the hydrocarbon feed stream to the reforming zone should preferably contain less than about 0.02 wt. percent of sulfur and preferably less than 0.01 wt. percent, a condition that is readily attainable when employing the process described above. As mentioned earlier, any of the conventional catalytic reforming processes that employ hydrogen atmospheres such as platforming and hydroforming may be used in carrying out the present process. The hydrogen produced within the catalytic reforming zone is recycled to this zone while a portion is passed to the hydroiining zone described earlier. It is a particular advantage of the present invention that it makes available hydrogen that contains very small amounts of hydrogen sulfide, in the order of less than about 0.1 vol. percent. Thus, the conversion and selectivity of the reaction within the catalytic reforming zone are maintained at unusually high levels.

The present invention may be best understood by zone 25.

reference to the attached figure. A heavy virgin naphtha containing about 0.3 wt. percent of sulfur and boiling within the range of about 200 to 330 F. is introduced through line 5 and pump 6 within hydroiining zone 8. In this instance with 200 s. c. f./bbl. of added hydrogenrich recycle gas, the naphtha feed is at a temperature of about 700 F. and is pressured by pump 6 to a pressure of about 600 p. s. i.g. This is the pressurel needed to keep the feed as a liquid in the presence of the hydrogencontaining recycle gas at a temperature slightly below its critical.

Hydrolining zone 8 may be operated at a temperature of about 700 F., a pressure of 600 p. s. i. g., a hydrocarbon feed rate of 2 volumes of feed (liquid) per volume of catalyst and with 200 s. c. f./bbl. of diluent gas. The diluent gas in this instance is hydrogen-rich recycle gas derived from a hydroforming operation to be described later herein.

The efuent vapors from hydroning zone S liow through line 9 and heat exchanger 10 where their temperature is reduced to a value of 575 F., which is about 10 F. below the critical temperature of the feed. The resulting mixture of hydrogen su'liide and condensed and uncondensed hydrocarbon constituents are then passed to high pressure separation zone 1.1. Uncondensed vapors and hydrogen sulfide are removed overhead from Zone 11 via line 12, are cooled in indirect heat exchangers 13 and 14 to a temperature of about 105 F. whereupon substantially all of the hydrocarbon constituents contained therein are condensed. The resulting stream is then passed through back pressure regulator 1S to low pressure separation zone 16 which in this case is operated at substantially atmospheric pressure. Uncondensed light hydrocarbons and hydrogen sulfide are removed overhead from zone 16 through line 17 and may be processed in lany desired manner as, for example, by passage through a conventional petroleum refinery light ends plant.

Condensed hydrocarbons within low pressure separation zone 16 are withdrawn through line 1S, are pressured to about 400 p. s. i. g. by pump 19, are passed through heat exchanger 13, and are blended with the liquid hydrocarbons that in turn are withdrawn from high pressure separation zone 11 via pressure regulator 20 and fline 21.

In this instance, it will be noted that about 73% of the combined liquid hydrocarbon stream produced by the processing stepsL described above is derived from the high pressure separation zone 11, and the remaining 27% of the combined stream is derived from low pressure separation zone 16.. It will also be noted that the liquid withdrawn from high pressure zone 11, upon flowing through pressure regulator 20, is reduced in pressure from 600 p. s. i. g. to 400 p. s. i. g. Furthermore, the stream from the high pressure zone is at a temperature of 575 F., while the stream from the low pressure zone is at 525 F.

The combined hydrocarbon stream in line 22, at a pressure of 400 p. s. i. g. and a temperature of 562 F., is heated within heating zone 23 to a temperature of 950 F. ,and is then passed through line 24 to catalytic reforming In the embodiment of the invention described herein, this latter zone may be considered to be a hydroforming zone operating at a temperature of about 900 F., a pressure of about 200 p. s. i. g., a feed rate of 0.1 to 5 volumes of liquid hydrocarbon per volume of catalyst per hour and hydrogen recycle rates of about 5000 s. c. f./bbl. of feed. The catalyst employed in this zone may be platinum or molybdena on alumina or any other conventional hydroforming catalyst.

The hydroformate product is withdrawn from catalytic reforming zone 25 through line 26 while the recycle gas, largely hydrogen, is recycled to zone 2S through lines 27 and 28. A portion of the recycle gas is passed, once through, to hydroiinng zone 8 through line 7.

The hydroformate produced in line 26 by the process described herein will generally contain less than 0.02 wt. per cent sulfur.

It will be understood that hydrocarbon feedstocks other than the heavy naphtha of the example described above may be employed in the process of the present invention. It may be applied in any case where a desulfurized feed is to be subsequently processed at high temperature. For example, light and heavy virgin and/or cracked naphthas can be processed in this manner; heating oil, kerosenes, diesel fuels, ,and distillate fuel oils, which are to be further processed, can also be handled by this process. Likewise, any conventional hydroning and catalytic reforming conditions, processes, and catalysts may be utilized without departing from the spirit or scope of the present invention.

Throughout the present description, it has been stated that a mixture of hydrocarbons will possess a definite critical temperature. It is realized that individual hydrocarbons actually possess individual critical properties and that a mixture of hydrocarbons therefore does not generally possess a single critical temperature. It is conventional in the art, however, to assume that such mixtures do possess individual critical temperatures, and it is in this sense that the present description uses this term.

What is claimed is:

l. A process for desulfurizing and increasing the quality of a sulfur-containing distillate petroleum fraction that has a critical temperature between 400 F. and 700 F. and that boils within the range of about 100 F. to 500 F., which comprises passing said petroleum fraction to a hydroning zone operating at temperatures of 500 F. to 750 F. and at a high enough pressure to keep the feed as a liquid at a temperature slightly less than its critical, whereby said sulfur compositions are substantially completely converted to hydrogen sulfide, cooling the hydroned fraction at substantially constant pressure to a temperature of about to 50 F. below the critical temperature of the feed to produce liquid hydrocarbon constituents and vaporized hydrocarbon constituents and hydrogen sulde, separating the liquid constituents from the vaporized constituents and hydrogen sulde in a high pressure separation zone, withdrawing said liquid constituents from said high pressure separation zone and adjusting their pressure to that of a catalytic reforming zone, withdrawing said vaporized hydrocarbon constituents and hydrogen sulde from said high pressure separation zone and cooling to a temperature suiicient to condense said vaporized hydrocarbon constituents at substantially atmospheric pressure, separating the resulting condensed hydrocarbon constituents from any non-condensed hydrocarbon constituents and hydrogen sulfide at substantially atmospheric pressure, adjusting the pressure of the condensate to that of said catalytic reforming zone, combining said liquid hydrocarbon constituents and said condensate, passing the combined said constituents and said condensate to said catalytic reforming zone to form a catalytic reformate and a hydrogen-rich gas, recycling a portion of said gas to said catalytic reforming zone and passing a second portion of said gas to said hydroning zone.

2. Process as defined in claim 1 wherein the petroleum fraction boils within the naphtha boiling range.

3. Process as defined in claim l wherein the petroleum fraction boils within the range of about 200 F. to 400 F.

4. A method of desulfurizing ,a sulfur-containing petroleum fraction boiling within the range of about F. to 500 F. and having a critical temperature of between 400 and 700 F. preparatory to feeding the fraction to a catalytic reforming zone which comprises passing said petroleum fraction to a hydroning zone operating at temperatures of 500 F. to 750 F. and at a high enough pressure to keep the feed as a liquid at a temperature slightly less than its critical, whereby said sulfur compositions are substantially completely converted to hydrogen sultide, cooling the hydrofined fraction at substantially constant pressure to a temperature of about 25 to 50 F. below the critical temperature of the feed to produce liquid hydrocarbon constituents and vaporized hydrocarbon constituents and hydrogen sulde, separating the liquid constituents from the vaporized constituents and hydrogen sulfide in a high pressure separation zone, withdrawing said vaporized hydrocarbon constituents and hydrogen sulfide from said high pressure separation zone and cooling to a temperature suiicient to condense said vap orized hydrocarbon constituents at substantially atmospheric pressure, separating the resulting condensed hydrocarbon constituents from any non-condensed hydrocarbon constituents and hydrogen sulfide at a substantially atmospheric pressure, and combining the said condensate with the said liquid hydrocarbon.

5. Process as defined in claim 4 wherein the petroleum fraction boils within the naphtha boiling range.

6. Process as deiined in claim 4 wherein the petroleum fraction boils within the range of about 200 F. to 400 F.

References Cited in the le of this patent UNITED STATES PATENTS 2,417,308 Lee Mar. 11, 1947 2,567,252 Strang Sept. 11, 1951 2,574,445 Porter et al Nov. 6, 1951 

1. A PROCESS FOR DESULFURIZING AND INCREASING THE QUALITY OF SULFUR-CONTAINING DISTILLATE PETROLEUM FRACTION THAT HAS A CRITICAL TEMPERATURE BETWEEN 400* F. AND 700* F. AND THAT BOILS WITHIN THE RANGE OF ABOUT 100* F. TO 500* F., WHICH COMPRISES PASSING SAID PETROLEUM FRACTION TO A HYDROFINING ZONE OPERATING AT TEMPERATURES OF 500* F. TO 750* F. AND AT A HIGH ENOUGH PRESSURE TO KEEP THE FEED AS A LIQUID AT A TEMPERATURE SLIGHTLY LESS THAN ITS CRITICAL, WHEREBY SAID SULFUR COMPOSITIONS ARE SUBSTANTIALLY COMPLETELY CONVERTED TO YDROGEN SULFIDE, COOLING THE HYDROFINED FRACTION AT SUBSTANTIALLY CONSTANT PRESSURE TO A TEMPERATURE OF ABOUT 25 TO 50* F. BELOW THE CRITICAL TEMPERATURE OF THE FEED TO PRODUCE LIQUID HYDROCARBON CONSTITUENTS AND VAPORIZED HYDROCARBON CONSTITUENTS AND HYDROGEN SULFIDE, SEPARATIING THE LIQUID CONSTITUENTS FROM THE VAPORIZED CONSTITUENTS AND HYDROGEN SULFIDE IN A HIGH PRESSURE SEPARATION ZONE, WITHDRAWING SAID LIQUID CONSTITUENTS FROM SAID HIGH PRESSURE SEPARATION ZONE AND ADJUSTING THEIR PRESSURE TO THAT OF A CATALYTIC REFORMING ZONE, WITHDRAWING SAID VAPORIZED HYDROCARBON CONSTITUENTS AND HYDROGEN SULFIDE FROM SAID HIGH PRESSURE SEPARATION ZONE AND COOLING TO A TEMPERATURE SUFFICIENT TO CONDENSE SAID VAPORIZED HYDROCARBON CONSTITUENTS AT SUBSTANTIALLY ATMOSPHERIC PRESSURE, SEPARATING THE RESULTING CONDENSED HYDROCARBON CONSTITUENTS FROM ANY NON-CONDENSED HYDROCARBON CONSTITUENTS AND HYDROGEN SULFIDE AT SUBSTANTIALLY ATMOSPHERIC PRESSURE, ADJUSTING THE PRESSURE OF THE CONDENSATE TO THAT OF SAID CATALYTIC REFORMING ZONE, COMBINING SAID LIQIUD HYDROCARBON CONSTITUENTS AND SAID CONDENSATE, PASSING THE COMBINED SAID CONSTITUENTS AND SAID CONDENSATE TO SAID CATALYTIC REFORMING ZONE TO FORM A CATALYTIC REFORMATE AND A HYDROGEN-RICH GAS, RECYCLING A PORTION OF SAID GAS TO SAID CATALYTIC REFORMING ZONE AND PASSING A SECOND PORTION OF SAID GAS TO SAID HYDROFINING ZONE. 